Steelmaking slag, which is separated by gravity difference, is lighter than iron and contains almost no heavy metals. Accordingly, steelmaking slag is less harmful and thus there is relatively active research into steelmaking slag to use as materials for construction. However, steelmaking slag contains free-CaO and thus volume thereof expands by chemical reaction occurring upon contact with water. Accordingly, cracks may occur when steelmaking slag is used as a material for road construction or concrete, thereby extremely limiting application thereof.
To commonly use steelmaking slag, a method of controlling a generation amount of free-CaO was developed and commonly used as a method to rapidly cool steelmaking slag at a molten state, using high-speed air. The steelmaking slag is also called atomizing steelmaking slag (ASS), since steelmaking slag produced according to the method has a globular shape. In addition, the steelmaking slag is called rapidly-cooled steelmaking slag (RCSS) since the steelmaking slag is prepared according to a rapid cooling process. In addition, steelmaking slag is commonly called as precious slag balls (PS ball).
PS balls do not contain free-CaO, thereby liminating any risk of collapse due to expansion. In addition, since PS balls have a fine aggregate shape similar to a globular shape, liquidity increases by ball bearing effects when used as a construction material for concrete. Furthermore, PS balls have higher density than other materials constituting concrete and, thus, attempts have been made to utilize PS balls in various use as road packing, weight balancing materials, and the like.
Meanwhile, general cement and cement products harden at a time point of 24 hours and then reach peak strength at the material age of 28 day. Like this, overall characteristics of general cement and cement products are exhibited from the material age and thereby quick-hardening cement and products using the same are used in emergency works such as roads, bridges, ports, sanitary pipe works, and the like.
General quick-hardening cement is prepared by mixing gypsum with clinker containing a quick-hardening mineral such as CaO.Al2O3, 12CaO.7Al2O3, 11CaO.7Al2O3.CaX, where X is a halogen element, and the like and then pulverizing, or by mixing pulverized materials of the quick-hardening minerals with ordinary Portland cement, gypsum and other additives (Korean Patent Application Pub. Nos. 76-397 and 90-33, and Japanese Patent Application Pub. Nos. 52-139819, 63-285114, and 64-37450).
However, to produce quick-hardening cement, clinker is prepared in a high-temperature firing furnace and thereby preparation cost is expensive, and it is difficult to control volatiles or molten elements and thereby properties of cement may be different according to preparation time. In particular, quick-hardening cement has volume change by crystal transition of ettringite (3CaO.Al2O3.3CaSO4.32H2O), which is one of hydrates generated through reaction with water and one of main hydrates exhibiting quick-hardening properties, due to a large amount of Al2O3, or an Al(OH)3 gel hydrate has reduced stability with respect to moisture. In addition, due to existence of sulfate, volume expansion occurs through reaction with SO3 ions. Such phenomena are considered drawbacks since stability of structures may be deteriorated in the long term.
As an advanced method to improve performance of such quick-hardening cement and stability of structures after hardening, a preparation method involving mixing pulverized materials of hauyne-based clinker containing calcium sulfo-aluminate, as a main material, with ordinary Portland cement, gypsum, slaked lime, and the like is known (Korean Patent Application Pub. Nos. 97-008685, 10-0220340, and 10-0310657).
Korean Patent No. 0310657 discloses a basic method of preparing quick-hardening cement, Korean Patent No. 0670458 discloses a method of preparing mortar utilizing quick-hardening cement, and Korean Patent No. 0755272 discloses a method of preparing quick-hardening cement and latex concrete.
However, since quick-hardening cement is generally hardened within several minutes or several dozen minutes through reaction with water during a preparation process of mortar or concrete, exhibits a strength of 20 MPa or more within 3 to 6 hours, and forms an initial cement structure. Accordingly, deformation, in the long term, by moisture evaporation may be minimized and a stable structure, in which few cracks are formed, may be formed, thereby being mainly used in emergency repair of structures such as roads, bridges, and the like. However, quick-hardening cement is not used in most presently developed mortars since most companies developing mortar have technical limitation with respect to quick-hardening cement, and thereby the companies specialize products by adding functional raw materials. Accordingly, there is need to develop a hydraulic binder having quick-hardening properties, without containing the functional elements.
Accordingly, although inventors of the present invention developed an ultra quick-hardening hydraulic binder through mixing PS ball powder with gypsum, the ultra quick-hardening hydraulic binder has problems such as deteriorated workability by initial high hydration heat reaction and initial coagulation of rapidly-cooled steelmaking reduction slag powder (PS ball), and reduced strength in the long term. Therefore, there are lots of problems in that the ultra quick-hardening hydraulic binder is used as a substitute of OPC while exhibiting quick-hardening performance.